Thermal printers in general use a thermal printing medium such as ink ribbon which has a hot-melt ink layer and is interposed between recording paper and a thermal head, so that the hot-melt ink on the ink ribbon is heated and melted by multiple heater elements attached to the thermal head, to transfer or print desired letters or symbols on the recording paper. Thermal printers have an advantage that the noise produced by the head hitting the paper during printing operation is extremely small than that of other type printers.
The use of thermal printers is today expanded to electronically-controlled typewriters in which correcting function is indispensable to correct letters or symbols once printed on printing paper. In this connection, most typewriters of this type include an erasing ribbon in addition to normal ink ribbon to effect correction by painting the letters to be erased by a colorant of the same color as the recording paper.
However, the use of specific erasing ribbon requires a changeover mechanism to selectively activate the ink ribbon or the erasing ribbon, and this invites a large-scaled and complicated construction of the typewriter. Beside this, since the painted colorant makes an uneven plane on the paper, clear print on the colorant is not expected.